A steam turbine is a rotary machine intended to convert the thermal energy in steam into mechanical energy in order to drive an alternator, a pump or any other rotary mechanical receiver. The turbine generally comprises a high-pressure module, possibly a medium-pressure module, and at least one low-pressure module. Steam supplied by a steam generator is conveyed to the high-pressure module then to the medium-pressure and low-pressure modules. The steam exhausted from the low-pressure modules is directed to a condenser, generally situated underneath the low-pressure modules. The remainder of the description is devoted to a device for a low-pressure module.
With reference to FIG. 1, which schematically illustrates, according to the prior art, an independent structure within which the structural work supports firstly the turbine and secondly the condenser, the low-pressure module 1 comprises an outer jacket 2 known as the exhaust box. Because the pressure of the steam on the exhaust side of the low-pressure module 1 is of the order of a few tens of mbar in the operational configuration, the exhaust box 2 and the outer jacket 3 of the condenser 4 together form an evacuated space. The low-pressure module 1 also comprises, inside the exhaust box 2, an internal turbine casing 5 with two streams, which may or may not be symmetric, containing a rotor 6 equipped with moving blades and supporting fixed vanes of the low-pressure module 1.
With reference to FIG. 2, which is an exploded perspective view of the exhaust box 2 and of the internal turbine casing 5, according to an independent structure of the prior art, the exhaust box 2 comprises a front part 7 and a rear part 8. The front part 7 comprises a lower part 7A and an upper part 7B which are bolted together at a mating plane 9. The same is true of the rear part 8, which comprises a lower part 8A and an upper part 8B which are bolted together at a mating plane 10, the two mating planes 9, 10 being continuous with one another. The exhaust box 2 encompasses the internal turbine casing 5 which is made up of a central part 11 and of two exhaust ends 12, 13, one of them, 12, at the front and the other, 13, at the rear. The central part 11 of the internal turbine casing 5 is intended to support at least one set of fixed vanes and to accommodate the rotor 6 equipped with at least one set of moving blades. The steam is let into the central part 11 via at least one pipe 14. The steam is then split into a front stream and a rear stream. The two streams expand in the central part 11 of the internal turbine casing 5, to drive the rotor 6. The steam is then directed toward the two, front 12 and rear 13, exhaust ends. Bearings 15 are incorporated into said exhaust ends 12, 13 to support the rotor 6 inside the internal turbine casing 5.
The exhaust box 2 is supported by the condenser 4, while the internal turbine casing 5 is supported by a slab 16 connected to a raft foundation 17 via posts 18, said raft foundation 17 resting on the ground 19. The connection between the internal turbine casing 5 and the slab 16 is via two bearers 20, one of them secured to the front exhaust end 12 and the other to the rear exhaust end 13 of said internal turbine casing 5. Thus, the internal turbine casing 5 is decoupled from the exhaust box 2, at its mount.
Despite the benefit of making the internal turbine casing and the exhaust jacket independent of one another in the region of the mounts that support said turbine casing, notably for the reasons mentioned hereinabove, it still remains the case that the connection between said internal turbine casing and the slab, using the bearers, has to have certain properties because this connection has to prevent accidental lifting of the internal turbine casing in the event, for example, of the untimely loss of a rotor blade, which will create an out-of-balance force, causing the rotor to become unbalanced and therefore react by lifting, causing the internal turbine casing to lift in relation to the slab. In addition, this connection between the internal turbine casing and the slab has to be configured to allow said internal turbine casing to slide along the slab in order to take turbine casing expansion into consideration. Specifically, because the internal turbine casing is immobilized at its front part, it will have a tendency to expand in the region of its rear part and, in order to allow for this expansion, it is necessary to allow for said turbine casing to slide with respect to the slab.
This type of connection, between the internal turbine casing and the slab, and which meets these two requirements, is already in use, but using separate means, the one designed specifically to prevent the turbine casing from lifting and the others specifically designed to allow the internal turbine casing to slide along the slab, said means being installed beside one another in the region of this connection. These existing connections occupy a great deal of space because of these multiple different means laid out in the region of the connecting interface where the turbine casing and the slab meet, and which are positioned side by side. In addition, these separate means need to be set out relative to one another in a special and well ordered geometry so that they do not interfere with one another and do not impair the quality of the connection. Finally, adjusting these separate means to ensure a good connection between the internal turbine casing and the slab is a lengthy process because it requires two sets of intervention, one on the special-purpose means that prevent the lifting and the other on the special-purpose means that allow the sliding. The connections used in devices for steam turbines according to the invention involve connectors of just one single type, each performing both functions, that of preventing the internal turbine casing from lifting and that of allowing said turbine casing to slide along the slab. Thus, the problems associated with the use of two special-purpose connectors each one dedicated to one particular function and which have been mentioned hereinabove are solved by the single connector involved in the devices for steam turbines according to the invention.